The present invention relates to fiber optic couplers and more particularly to a low-cost method of making fiber optic couplers.
Certain types of fiber optic systems require couplers in which at least a portion of the light propagating in one fiber is coupled to one or more other fibers.
It has been known that coupling occurs between two closely spaced cores in a multiple core device. The coupling efficiency increases with decreasing core separation and, in the case of single-mode cores, with decreasing core diameter. There have been developed a number of couplers that are based on these principles.
Multimode and single-mode couplers have been formed by positioning a plurality of fibers side-by-side along a suitable length thereof and fusing the claddings together to secure the fibers and reduce the spacings between the cores. Coupling can be enhanced by stretching and rotating the fibers along the fused length thereof as taught in U.S. Pat. No. 4,426,215. Also, a portion of the cladding is sometimes removed by etching or grinding to decrease the intercore distance as taught in U.S. Pat. No. 4,449,781. These processes are labor intensive and do not always result in the formation of couplers exhibiting predetermined coupling characteristics. This latter mentioned disdvantage is particularly apparent in the manufacture of certain single-mode couplers wherein the coupling core sections are to remain linear.
Said copending Keck et al. Application teaches a method wherein there is initially provided a coupler preform having a plurality of spaced glass cores extending through a matrix of glass having a refractive index lower than that of the glass cores. The coupler preform is heated and stretched to form a glass rod which is severed into a plurality of units. Heat is applied to the central region of each unit while the ends are pulled to elongate and taper inwardly the heated central region thereof. Various techniques are taught for providing the coupler with interconnection fibers.